To Investigate the Prognostic Value of Oxygen Uptake in Weaning of Patients From Prolonged Mechanical Ventilation

1.Research hypothesis: during weaning patient from prolonged mechanical ventilation, if the work load caused by weaning was below the patient's AT, oxygen uptake will be constant. Otherwise, if the work load was above the patient's AT, the oxygen uptake will increase.

1. Patient: who have tracheostomy tubes and with prolonged mechanical ventilation
2. Measurement: oxygen uptake(V̇O2) and respiratory mechanics during the spontaneous breathing trials
3. Outcome: Correlation between the oxygen uptake(V̇O2) and the weaning outcome

2.Specific aims:

1. to investigate the prognostic value of oxygen uptake in weaning patients from prolonged mechanical ventilation
2. Subgroup analysis may suggest which weaning protocol potentially benefit the most for each population group (cardiovascular disease, chronic pulmonary disease, neuromuscular disease, cerebrovascular disease)